The present invention relates to a developing device employed in an electrophotographic recording system and more particularly to a device for detecting a remaining level of toner which develops an electrostatic latent image formed on a photosensitive drum into a visible image. By detecting the toner level, a user can then supply additional toner to the interior of the system at an optimal time.
It is commonly known that typical electrophotographic recording apparatuses such as copying machines, laser beam printers, etc. form an invisible electrostatic latent image on the surface of a photosensitive drum. Toner, which is made of a carbon powder component and supplied to the surface of the photosensitive drum to visualize the electrostatic latent image, can then be transferred and fixed onto a printable medium, such as paper, to form a hard copy of the electrostatic image. The electrophotographic recording apparatus typically includes a hopper which contains the toner, and a toner detecting device installed within the hopper for sensing a remaining amount of toner. It is well known to those skilled in the art that one of the representative methods for detecting the remaining amount of toner is a method using a toner sensor, for example, a piezoelectric sensor. We have found that equipment requiring a piezoelectric sensor tends to be uncompetitively expensive, however, due to the cost of the piezoelectric sensor.